Abstract Alzheimer's disease (AD) is a debilitating neurodegenerative disorder and the most common form of dementia in elderly. It is characterized by progressive impairment of memory and cognitive functions and typically leads to death within 3-9 years after the diagnosis. Despite the severity of this disease, there is no disease modifying therapies for AD. Thus, it is essential to identify mechanisms and critical targets that can be manipulated to reverse or slow AD progression. The main objective of this AD supplement application is to test the novel idea that the mitochondrial Ca2+ uniporter (MCU) plays an important role in AD pathogenesis, and that deletion of MCU would provide neuroprotection and correct behavioral abnormalities, using a mouse model of AD. This idea stems from several important observations made through research funded by the parent grant R01 NS 096246. Specifically, we found that MCU deletion (1) protects neurons from glutamate-induced Ca2+ deregulation and excitotoxicity, (2) prevents hyperexcitability of neural networks and induction of generalized seizures, and (3) enhances GABAergic synaptic activity, which is likely responsible for the anticonvulsant effect of MCU knockout (KO). Importantly, MCU KO mice did not show any motor, sensory or cognitive behavioral abnormalities. Although the parent grant is not focused on AD and AD-related dementia (ADRD), our findings are highly relevant to AD and ADRD. Indeed, triggered by the pathological accumulation of amyloid-? (A?) peptides and the downstream pathogenic events, Ca2+ deregulation and Ca2+-dependent excitotoxicity are thought to be the key mechanisms that ultimately lead to synaptic dysfunction and neuronal loss in AD. In addition, neural network abnormalities, hyperexcitability and seizures observed in AD patients and AD mouse models, play an important role in the pathogenesis of AD/ADRD. Given that MCU KO prevents both excitotoxicity and network hyperexcitability, we propose that MCU deletion will correct cellular and behavioral abnormalities in a mouse model of AD. Our central hypothesis is: MCU plays a key role in the pathogenesis of AD, and MCU deletion will prevent synaptic dysfunction and excitotoxicity, and correct behavioral abnormalities in a mouse model of AD. We will use state-of-the-art approaches including multiphoton microscopy, brain slices electrophysiology and behavioral testing in new transgenic mouse models to test our hypothesis in two specific aims. Aim 1 will determine whether MCU deletion prevents neurodegeneration and alleviates cognitive deficits in the context of AD. Aim 2 will determine whether MCU deletion prevents Ca2+ deregulation and synaptic dysfunction in the context of AD. The proposed research is expected to establish the role of MCU in multiple aspects of AD pathogenesis including Ca2+ deregulation, synaptic impairment and neurodegeneration, and may ultimately lead to the development of new disease-modifying strategies for treating AD, which are based on targeting MCU and other mitochondrial Ca2+ transporters.